The present invention relates generally to inflator compositions and more particularly to solid inflator compositions useful as gas generators. Gas generating compositions must satisfy various criteria for optimal effectiveness. Gas generating compositions for use in vehicle occupant restraints, e.g., automobile or aircraft airbags must satisfy stringent criteria including toxicity requirements which are of concern in solid propellants for military or propulsion systems. Conventional gas generating compositions are plagued with problems, including a high pressure exponent, a low burning rate, poor combustion stability, and inadequate age-life stability. The inferior ballistic properties disadvantageously result in low gas yields and unburned, energetic residues which remain at the end of the normal burn interval. Not surprisingly, great demand has recently arisen for gas generating compositions which yield a high volume of gas and a low volume of solid particulates, and which exhibit a low pressure exponent and have low pressure combustion stability.
Attempts to improve existing gas generating compositions to impart these properties have been unsuccessful for various reasons. For example, the addition of certain modifiers such as organometallic and certain oxides produce exhaust products that are toxic in man-rated environments. Other additives previously utilized, while not producing toxic exhaust products, have not successfully improved low pressure combustion efficiency. Also, other traditional techniques to solve these problems involve the use of relatively expensive degflagrative additives that interfere with the thermal or chemical stability of the overall formulation during long term thermal soak or thermal cycling conditioning.
Those skilled in this art have experienced difficulty in selecting among the many possible additive candidates for gas generating compositions intended for airbag applications to obtain compositions where smoke and ash are considered unacceptable consequences.
Moreover, propellant compositions are typically compacted into the form of grains of a suitable shape. Such propellant grains must be capable of sustaining thermal and tensile shock during igniter functioning, and must exhibit sufficient strength to remain intact during gas generator functioning if ballistic performance is to remain unaffected. The grains must retain such capability after aging and cycling.
There exists a continuing need for gas generating compositions, particularly gas generating compositions for air bag utility, which exhibit a low pressure exponent, high burning rate and good combustion efficiency at low pressures.